We're living longer — that's no surprise. But what is astonishing is just how much longer we're living than our predecessors, and how short of a time it's taken to happen. According to new research in PNAS, the last four generations of humans have seen an improvement in mortality that outdoes any of the previous 8,000 generations.

The research compared modern human lifespans with ethnographically researched hunter-gatherer tribes, and they found that youth mortality is now 200 times lower than it was in 1900. In fact, the changes are so dramatic, that a 30-year-old hunter-gatherer had the same mortality rate as a modern 72-year-old.

Overall, life expectancy was boosted by about 165% from hunter-gatherers to modern Swedes, which amounts to an improvement of 12% per generation. The bizarre thing is that the average lifespan of a hunter-gatherer was actually closer to that of a chimpanzee than a modern human. The concerted improvement in human lifespans really took off in the early 20th century, as the researchers point out:

Before the late 1800s, even humans in the lowest-mortality nations were not experiencing mortality much lower than was typical during most of human evolution.

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This level of mortality reduction is unique, and is thought to be linked to environmental improvements. Food and medical treatment are now available on levels never before imagined, and it raises questions if the same dramatic improvements can happen with other species, and if the extension of the human lifespan will continue at this same pace. As the authors conclude:

What is the underlying explanation for this extraordinary plasticity? Why does the human genome give humans a license to drastically reduce mortality by nongenetic change? Are other species capable of comparable levels of plasticity? For how long will life expectancy continue to rise and by what means?